US physicians wrote 4.4 million prescriptions last year for nitroglycerin (TNG) tablets, those tiny pills in the tiny bottle that dissolve under the tongue and act in minutes to relieve chest pain associated with coronary artery disease.

TNG has direct vasdilatory effects on the coronary arteries. It also reduces blood pressure and cardiac “preload.” Patients take TNG when they first feel angina. They can take up to 3 if the first one doesn’t work. After that, they call 911.

TNG has been around forever, and it turns out that’s a problem. The pills predate the Food and Drug Administration itself, and were grandfathered-in as safe and above regulatory review in 1938 when the agency was formed.

The result is that 80% of the TNG prescribed in the US has never been tested for safety, potency or effectiveness. The only form of TNG that has received FDA approval is Nitrostat, which is made by Pfizer.

Amazingly, doctors just found this out last month. It’s possible that millions of patients may have been taking substandard or ineffective forms of the drug. Some of them may have been harmed by the oversight.

“If it’s not approved and no one has tested it, we can’t be sure that it’s safe and effective,” Harry Lever, a cardiologist at the Cleveland Clinic told the New York Times.

Late last month, the FDA warned the 2 other TNG makers to cease marketing their unapproved products. The companies, Konec Inc. of Tucson and Glenmark Generics Inc. of Mahwah, NJ have been given 90 days to halt production, and 180 days to stop shipping them. Spokespeople from these companies said they’d comply, but insisted their products were safe.

Meanwhile Pfizer has ramped-up production of Nitrostat and claims it can handle the windfall.